The invention relates to multi-layer compositions comprising a fluoropolymer and a curable elastomer as well as to methods of producing same. In another aspect, this invention relates to methods of improving the adhesion between a fluoropolymer and other dissimilar materials, such as, epichlorohydrin and nitrile-butadiene elastomers.
Fluorine-containing polymers (i.e., fluoropolymers or fluorinated polymers), are an important class of polymers that include, for example, fluoroelastomers and fluoroplastics. Among this broad polymer class are polymers of high thermal stability, polymers of extreme toughness, and polymers exhibiting usefulness along a broad range of temperatures. Many of these polymers also are almost totally insoluble in a wide variety of organic solvents; see, for example, F. W. Billmeyer, Textbook of Polymer Science, 3rd ed., pp. 398-403, John Wiley and Sons, New York (1984).
Fluoroelastomers, particularly the copolymers of vinylidene fluoride with other ethylenically unsaturated halogenated monomers such as hexafluoropropene, find particular utility in high temperature applications, such as in seal gaskets and linings. See, for example, Brullo, R. A., xe2x80x9cFluoroelastomer Rubber for Automotive Applications,xe2x80x9d Automotive Elastomer and Design, June 1985, xe2x80x9cFluoroelastomers Seal Up Automotive Future,xe2x80x9d Materials Engineering, October 1988, and Grootaert, W. M., Millet, G. H., Worm, A. T., xe2x80x9cFluorocarbon Elastomers,xe2x80x9d Kirk-Othmer, Encyclopedia of Chemical Technology, 4th ed., Vol. 8, pp. 990-1005, John Wiley and Sons, New York (1993).
Fluoroplastics, particularly polychlorotrifluoroethylene, polytetrafluoroethylene, copolymers of tetrafluoroethylene and hexafluoropropylene, and poly(vinylidene fluoride), have numerous electrical, mechanical, and chemical applications. Fluoroplastics are useful, for example, as wire coatings, electrical components, seals, and in solid and lined pipes and piezoelectric detectors. See, for example, xe2x80x9cOrganic Fluorine Compounds,xe2x80x9d Kirk-Othmer, Encyclopedia of Chemical Technology, Vol. 11, pp. 20, 21, 32, 33, 40, 41, 48, 50, 52, 62, 70, and 71, John Wiley and Sons, New York (1980).
Multi-layer constructions containing a fluorinated polymer enjoy wide industrial application; multi-layer fluoropolymer constructions find utility in, for example, fuel line hoses and related containers and hoses or gaskets in the chemical processing field. Increased concerns with evaporative fuel standards give rise to a need for fuel system components that have increased barrier properties to minimize the permeation of fuel or fuel vapors through automotive components, such as fuel filler lines, fuel supply lines, fuel tanks, and other components of the engine""s fuel or vapor recovery systems. Various types of tubing have been proposed to address these concerns.
Adhesion between the layers of a multi-layered article may need to meet various performance standards depending on the use of the finished article. A variety of methods can be used to increase the adhesion between a fluorinated polymer layer and a non-fluorinated polymer layer. An adhesive layer can, for example, be added between the two polymer layers. U.S. Pat. No. 5,047,287 (Horiuchi et al.) discloses a diaphragm, suitable for use in automotive applications, that comprises a base fabric having bonded to at least one surface a fluororubber layer by an adhesive that includes an acrylonitrile-butadiene or acrylonitrile-isoprene rubber having an amino group. Blends of the fluoropolymer and the non-fluorinated polymer layer themselves are in some cases employed as an intermediate layer to help bond the two layers together. European Patent Application 0523644 (Kawashima et al.) discloses a plastic laminate having a polyamide resin surface layer and a fluororesin surface layer. The reference recognizes the difficulties encountered when making laminates having a polyamide layer and a fluororesin layer because of the incompatibility of the two materials. The laminate of the reference is prepared by use of an intermediate layer composed of a blend of an aliphatic polyamide resin with a fluorine-containing graft copolymer. U.S. Pat. No. 5,242,976 (Strassel et al.) discloses co-extruding vinylidene polyfluoride with an alkyl polymethacrylate and vinylidene polyfluoride composition.
Surface treatment of one or both of the layers sometimes is employed to aid bonding. Some, for example, have taught treating fluoropolymer layers with charged gaseous atmosphere and applying subsequently a layer of a second material, for example a thermoplastic polyamide. E.g., European Patent Applications 0185590 (Ueno et al.) and 0551094 (Krause et al.) and U.S. Pat. No. 4,933,060 (Prohaska et al.) and U.S. Pat. No. 5,170,011 (Martucci).
Numerous methods of bonding have been proposed for multi-layer constructions where the fluoropolymer layer contains a molecular structure resulting from the inclusion of a vinylidene fluoride (VDF) or similar monomer unit. Similar monomers in this sense mean those monomers other than VDF which when polymerized, form monomer sequences similar to polymerized vinylidene fluoride. In general, these fluoropolymers will readily dehydrofluorinate when exposed to a base. As a result, such fluoropolymers undergo relatively facile adhesion promoting reactions. These other such monomers include ethylenically unsaturated monomers which, when incorporated into fluoropolymers, can produce a similar (including an identical) polymeric microstructure as the polymerized VDF. These similarly formed polymers are also prone to dehydrofluorination and subsequent adhesion promoting reactions. In general, the microstructure of a hydrogen bonded carbon atom between fluorine bonded carbon atoms creates a site reactive to a base. The reactivity of a hydrogen bonded carbon is further enhanced when its carbon atom is adjacent to, or attached to a carbon atom possessing a carbon bonded xe2x80x94CF3 group (supplied by HFP or 2-hydropentafluoropropylene for instance) or another electron withdrawing group. Monomers suitable for forming such hydrogen-bonded-carbon reactive sites include, but are not limited to, VDF, 1-hydropentafluoropropene, 2-hydropentafluoropropene, and trifluoroethylene.
The addition of a primary amine containing unsaturated compound to a hydrocarbon elastomer layer is disclosed as a method for increasing the adhesion to a layer comprising fluoropolymer comprising interpolymerized units derived from vinylidene fluoride in U.S. Pat. No. 5,512,225 (Fukushi).
Multi-layer constructions containing a fluoropolymer without the VDF segment or a similar easily dehydrofluorinated segment as discussed above and below, are much more difficult to make with adequate interlayer bond strength. These types of construction are desirable however, because fluoropolymers without a segment readily susceptible to dehydrofluorinating are more chemically inert. For example, tubes or hoses or other containers used in fuel or chemical applications where inertness, permeation reduction and interlayer adhesion improvement are important, will benefit from the improvement described in this invention.
As the above discussion illustrates, the combined features of curable elastomer compounds and fluoropolymer materials are a desirable combination, particularly when the fluoropolymer possesses improved chemical resistance or permeation properties.
In one aspect, this invention relates to a method of bonding a fluoropolymer to a curable elastomer comprising the steps of: a) providing; (i) a fluoropolymer layer comprising a fluorine-containing polymer derived from interpolymerized units of at least one fluorine-containing olefinically unsaturated monomer, with the proviso that if a perfluorinated monomer is present then at least one monomer that contains hydrogen atoms is also present and with the further proviso that the monomer(s) include neither vinylidene fluoride nor a monomer which when polymerized forms a micro structure similar to polymerized vinylidene fluoride, (ii) a curable elastomer, and (iii) a dehydrofluorinating composition, b) forming a layer comprising a mixture of the curable elastomer and an effective amount of the dehydrofluorinating composition, c) forming a multi-layer article by contacting the layer of the mixture with the layer comprising the fluoropolymer, and d) curing the multi-layer article under conditions sufficient to provide an interlayer adhesion between the curable elastomer layer and the fluoropolymer layer of at least 2 Newtons per cm of width. The dehydrofluorinating composition is preferably selected from the group consisting of at least one of an organo-onium and an amidine. The curable elastomer is preferably selected from the group consisting of at least one of an epichlorohydrin-containing elastomer, a nitrile rubber-containing elastomer, ethylene propylene diene copolymers, silicone-containing elastomers, fluoroelastomers, and mixtures thereof.
In another aspect, the invention relates to a method of bonding a fluoropolymer to a curable elastomer comprising the steps of: a) providing; (i) a layer of a fluoropolymer comprising a copolymer derived from interpolymerized units of a first monomer selected from the group consisting of hexafluoropropylene, a perfluoroalkyl vinyl ether, a branched perfluorinated monomer, and combinations thereof, a second monomer selected from the group consisting of tetrafluoroethylene, chlorotrifluoroethylene, a fully halogenated olefinically unsaturated monomer containing two carbon atoms and combinations thereof, a third monomer selected from the group consisting of ethylene, propylene, a non-halogenated olefinically unsaturated monomer and combinations thereof, (ii) a curable elastomer, and (iii) a dehydrofluorinating composition, b) forming a layer comprising a mixture of the curable elastomer and an effective amount of the dehydrofluorinating composition, c) forming a multi-layer article by contacting the layer of the mixture with the layer comprising the fluoropolymer, and d) curing the multi-layer article under conditions sufficient to provide an interlayer adhesion between the curable elastomer layer and the fluoropolymer layer of at least 2 Newtons per cm of width.
In still a further aspect, this invention relates to a method of bonding a fluoropolymer to a curable elastomer comprising the steps of: a) providing; (i) a layer of a fluoropolymer comprising a copolymer having a hexafluoropropylene monomer content of at least 22% by weight and an ethylene monomer content of at least 14% by weight wherein said copolymer is derived from interpolymerized units comprising hexafluoropropylene, tetrafluoroethylene, and ethylene, (ii) a curable elastomer, and (iii) a dehydrofluorinating composition, b) forming a layer comprising a mixture of the curable elastomer and an effective amount of the dehydrofluorinating composition, c) forming a multi-layer article by contacting the layer of the mixture with the layer comprising the fluoropolymer, and d) curing the multi-layer article.
Another aspect of the invention relates to a layered article comprising a first and second layer in intimate contact with one another. The first layer comprises a fluoropolymer substantially free of interpolymerized units derived from vinylidene fluoride or monomers which give a similar microstructure when polymerized. The second layer comprises a mixture of a curable elastomer and a dehydrofluorinating composition. The interlayer adhesion between the first layer and the second layer is at least 2 Newtons per cm of width. The a fluoropolymer used in the first layer may also be a fluorine-containing polymer derived from interpolymerized units of at least one fluorine-containing olefinically unsaturated monomer, with the proviso that of a perfluorinated monomer is present then at least one monomer that contains hydrogen atoms is also present and with the further proviso that the monomer(s) include neither vinylidene fluoride nor a monomer which when polymerized forms a micro structure similar to polymerized vinylidene fluoride.
The invention also relates to a layered article comprising a first layer comprising a fluoropolymer derived from interpolymerized units comprising hexafluoropropylene, tetrafluoroethylene, and ethylene, and a second layer comprising a mixture of a curable elastomer and a dehydrofluorinating composition. The first and second layers are in substantial contact with each other. The interlayer adhesion between the first and second layers is at least 2 Newtons per cm of width.
The layers discussed herein are intended to include the concept of a surface, such as that found when constructing a multilayered hose or other shaped article and not intended to be limited to flat shapes. Thus, a first layer or surface may be formed or shaped prior to application of the second material. The substantial contact of the second material to the first is to a surface of the first material. Either the fluoropolymer component or the curable elastomer component may be formed or shaped first. When a shaped article, such as a hose, is formed, either material may be on the inside or the outside of the article depending upon the intended use, such as where the temperature resistance or chemical resistance is most needed.
An additional aspect of the invention also relates to a layered article comprising a first layer comprising a fluoropolymer derived from interpolymerized units comprising hexafluoropropylene, tetrafluoroethylene, and ethylene and a second layer comprising a mixture of a curable elastomer and a dehydrofluorinating composition. The fluoropolymer used in the first layer has a hexafluoropropylene monomer content of at least 22% and an ethylene monomer content of at least 14%. The two layers are in substantial contact with each other.
An additional aspect of the invention relates to a layered article comprising a first layer comprising a fluoropolymer having a melt point of no more than 190xc2x0 C. derived from interpolymerized units comprising hexafluoropropylene, tetrafluoroethylene, and ethylene and a second layer comprising a mixture of a curable elastomer and a dehydrofluorinating composition. The two layers are in substantial contact with each other.
Examples of articles contemplated by this invention include a hose, a container, a gasket or a film.